The exhaust gas of a diesel engine or gasoline engine or other internal combustion engine, for example, contains carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NOx), particulate matter (PM), etc.
An internal combustion engine is provided with an exhaust treatment device for removing these constituents. The exhaust treatment device includes an oxidation catalyst for oxidizing the carbon monoxide etc., an NOx storage reduction catalyst or NOx selective reduction catalyst for removing the nitrogen oxides, a particulate filter for removing particulate matter, etc.
To raise the temperature of the exhaust treatment device which is arranged in the engine exhaust passage, it is known to make the unburned fuel burn in the engine exhaust passage. Japanese Patent Publication (A) No. 06-117239 discloses a catalyst warmup device which is provided with a catalyst converter which is provided in the exhaust system of the internal combustion engine, a spark plug which is arranged upstream of the catalyst converter of the exhaust system, and a hydrogen generation device for feeding hydrogen near the spark plug. It is disclosed that in this catalyst warmup device, when the catalyst temperature of the catalyst converter becomes a predetermined value or less, hydrogen is fed to near the spark plug and is ignited.